Adjustable sliding brush transformer and method of producing a brush track therefor



Nov. 11, 1969 H. J. PROXMIRE 3,478,290 NG BRUSH TRANSFORMER AND METHOD OF THEREFOR ADJUSTABLE S LIDI PRODUC NG A BRUSH TRACK 2 Sheets-Sheet l Filed Nov. 16, 1967 [17ventar Harry lay/ 7 Nov. 11, 1969 Filed Nov. 16, 1967 H. J. PROXMIRE 3,478,290

ADJUSTABLE SLIDING BRUSH TRANSFORMER AND METHOD OF PRODUCING A BRUSH TRACK THEREFOR 2 Sheets-Sheet 2 sill I F l 3x fn ventar: Harry J- Praxm/re,

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Patent 3,478,290 ADJUSTABLE SLIDING BRUSH TRANSFORMER AND METHOD OF PRODUCING A BRUSH ,TRACK THEREFOR Harry J. Proxmire, Fort Wayne, Ind., assignor to General Electric Company, a corporation of New York Filed Nov. 16, 1967, Ser. No. 683,627 Int. Cl. H01f 29/06, 27/30 US. Cl. 336-149 2 Claims ABSTRACT OF THE DISCLOSURE An adjustable sliding brush transformer with a reliefpolished brush track. The brush track is formed of a series of convex contact surfaces on successively disposed adjacent wire turns. The series of convex contact surfaces is underspanned by a series of concave surfaces of resin insulating material along the brush track. Electrical contact between the brush and the winding is achieved by sliding movement of the brush along the convex contact surfaces. The concave-convex brush track is produced by relief polishing a preselected portion of the winding. A polishing disc consisting of a mat of glass fibers or fibers of thermoplastic polyamide impregnated with silicon-carbide grit may be used.

Background of the invention This invention relates generally to adjustable sliding brush transformers and more particularly to adjustable sliding brush transformers having an improved brush track arrangement and to a method for producing brush tracks for adjustable sliding transformers.

Conventional adjustable sliding brush transformers consist of a transformer winding wound on a suitable magnetic core, usually of annular configuration. Generally the transformer is arranged to function as an autotransformer and includes a brush holder carrying one or more electrical brushes that slide across and make electrical contact with a brush track. To vary the output voltage of the transformer, the position of the brushes with respect to the brush track is changed either manually or by a motor.

In the manufacture of such prior art adjustable sliding brush transformers, insulated wire is wound on the annular core, and the brush track is formed by lapping or grinding the portions of the insulated winding to be contacted to remove the insulation therefrom and to provide a fiat contact surface for the brushes. Heretofore it has been assumed that it is necessary to provide a flat planar surface on the conductor of the insulated wire in order to provide suitable surfaces for making electrical contact with the brushes.

It will be appreciated that in the process of lapping or grinding not only is a portion of the insulation coating of the winding removed but appreciable amounts of the.

conductor material. In many instances, as much as one third of the cross-sectional area of metallic conductor of the insulated wire is removed in the process of forming the brush track. A common difliculty experienced in lapping or grinding, particularly in transformer designs with a conductor wire of .0201 of an inch or less in diameter, is that misaligned conductors may be either undercut or overcut in the process. As a result, such transformers during manufacture are rejected as failing to meet quality standards and must be reworked or scrapped.

, Another disadvantage of such conventional lapping and grinding techniques for producing a brush track or adjustable sliding brush transformer is that lapping and grinding is a relatively expensive step in the process of manufac- Fee ture. It is, of course, desirable to reduce the cost of manufacturing a product and to improve its quality and performance.

, Accordingly, it is a general object of my invention to Summary of the invention In accordance with one form of my invention, I have provided an adjustable sliding brush transformer comprising a core of magnetic material having a winding of successively disposed adjacent wire turns wound on the core. The winding is formed with a relief-polished brush track including a series of convex contact surfaces on successively disposed adjacent wire turns. Insulating resin material is disposed between the turns that form the series of convex contact surfaces and defines a series of concave surfaces along the brush track underspanning the convex contact surfaces. The adjustable sliding brush transformer includes at least one electrical brush for sliding electrical contact with the convex contact surfaces of the winding whereby electrical contact between the brush and the winding is achieved by sliding movement of the brush along the convex contact surfaces.

According to another aspect of the invention the brush track for the core and coil assembly of the improved adjustable sliding brush transformer is produced by relief polishing a portion of the winding whereby a portion of the insulation coating on the wire is removed to expose the metallic conductor and form a contact surface. A substantially greater amount of resin between the adjacent turns is removed than metallic conductor to form the brush track on the winding. Preferably, a polishing disc formed of glass fibers or of a mat of fibers of thermoplastic polyamide impregnated with silicon-carbide grit is used to polish the brush track to the desired convexconcave configuration.

An important advantage of the present invention is that it is possible in an adjustable sliding brush transformer having a winding of relatively small wire size to provide a brush track characterized by longer service life. Moreover, the brush track can be readily and inexpensively produced as compared with prior art tech niques.

The subject matter which I regard as my invention is set forth in the appended claims. The invention itself, however, together with further objects and advantages thereof may be better understood by referring to the following description taken in connection with the accompanying drawings in which:

Briefdescription of the drawings FIGURE 1 is-a perspective view of an adjustable sliding brush transformer embodying one form of the present invention; I

FIGURE 2 is an enlarged fragmentary cross-sectional I view taken along lines 22 of FIGURE 1;

Description of the preferred embodiments Referring now more specifically to FIGURES 1 and 2 of the drawings, I have illustrated therein an adjustable sliding brush transformer embodying one form of my invention. The adjustable sliding brush transformer 10 has an annular core ll-made by winding a ribbon or sheet of magnetic iron or steel. The annular core 11 is enclosed in two generally cup-shaped winding forms 12, 13 made from insulating material, such as plastic. The forms 12, 13 serve as a shell to insulate a winding 14 of successively disposed adjacent turns wound over the forms 12, 13 and may have serrations (not illustrated) along the outer edges to provide guides for placing and holding the insulated wire 15 of the winding 14.

For a more detailed description of the construction of adjustable sliding brush transformers of the type in which the presentinvention may be utilized, reference may be had to U.S. Patent No. 3,160,841 granted to J. P. Stefani et al., U.S. Patent No. 3,160,842 granted to C. A. Neumann et al., and U.S. Patent No. 3,185,948 granted to H. I. Helberg, all assigned to the assignee of the present invention.

The winding 14 on the adjustable sliding brush transformer 10 is formed by winding insulated wire about the annular core 11. A brush track 16 is provided on the outer surface of winding 14 for engagement with a brush 17 carried by a brush holder 18. Although in the illustrated embodiment of my invention the brush track 16 lies in a plane substantially perpendicular to the longitudinal axis of the winding 14, it will be appreciated that the brush track may be placed at other locations, as for example, along the outer cylindrical surface of the winding.

The brush 17 is conventionally constructed from a high resistance carbon or graphite type material to prevent excessive current flow when adjacent turns of the winding 14 are short circuited. It will be seen in FIGURE 1 that the brush holder 18 is secured to a rotatable shaft 19 extending through an opening in the core 11. In order to maintain a predetermined amount of contact with the brush track 16, the brush is urged against it by a spring means 20. The shaft 19 may have mounted thereon a knob 21 to allow manual turning of the shaft for varying the position of the brush 17 along the brush track 16.

Turning now to FIGURE 2, I have illustrated therein one form of my improved brush track arrangement. It will be seen that the individual conductors of the winding are bonded to the insulating forms 12, 13 by a resin material 22, such as an epoxy resin. The brush track 16 includes a series of convex contact surfaces 23, which in the illustrated embodiment of my invention were formed by relief polishing the winding 14 to dislodge portions of the insulation coating 24 of the winding 14 and expose the metallic conductor '25 so that an electrical contact between the brush 17 and the winding 14 is achieved by sliding the brush 17 into engagement with the metallic conductor 25 of the convex contact surface 23. It will be noted that as long as the contact surfaces 23 are not worn down by the sliding action of the brush 17, the contact established between the brush 17 and individual convex contact surfaces 23 is essentially linear.

In the process of relief polishing the winding 14, substantially greater amounts of insulating resin material 22 are removed than metallic conductor 25. As a result, the resin material 22 along the track 16 presents a series of concave surfaces26 that underspan the series of convex contact surfaces 23. An advantage of this arrangement is that an undercut commutating brush track is achieved without having to individually grind down the insulating material between the contact surfaces 23.

In FIGURE 3 I have illustrated a commonly used brush track arrangement of the prior art. The brush track 28 is formed by removing the insulation from the insulated wire 29 by grinding and lapping so as to provide a series of relatively flat contact surfaces 30 for travel of the brush 31. In order to obtain the desired flat contact surfaces 30, an appreciable quantity'of metallic conductor 32 is removed. To augment brush track life, the contact surfaces 30 may be plated with a layer of a corrosion resistant metal or alloy, such'as gold.

It will be noted that along the brush track 28 shown in FIGURE 3, the resin material 33 between' the fiat contact surfaces 30 is generally flush with the flat contact surfaces 30. As wear occurs on the contactsurfaces 30, it will be apparent that the brush 31 when moved over the surface of the resin material 33 will dislodge particles of the resin-material 33, and the contact surfaces 30 and the brush will become contaminated with the particles. v f

I have found that in adjustable sliding transformers that use conductor wire of relatively smaller sizes" the contact surfaces of the brush track do not have to be flat to provide satisfactory performance and service life. Also, economies in the manufacture and improvedperformance can be achieved by a method of relief polishing which I will now more fully described.

Having more specific reference now to FIGURES 4 and 5, I have illustrated therein the improved-method of producing a brush track for an adjustable sliding brush transformer as exemplified in a-turntable apparatus -36. The apparatus 36 is comprised of a turntable 37 rotatably supported on a frame 38, a first and a secondmandrel assembly 39, 40, a mandrel drive motor 41, and'apolisher assembly 42.

To carry out the steps of the method for producing a brush track, an operator stands at the left side of the apparatus 36 as viewed in FIGURE 4 or adjacent to the loading and unloading station. At this station controls (not shown) are conveniently positioned so that the operator can cause the turntable torotate 180 degrees to move a core and winding assembly 48 from the loading and unloading station to the polishing-station.

When the turntable 37 is in a position shown in FIG- URE 1, polishing disc 43 of the polisher assembly 42-is lowered into engagement with the portion of the winding on which the brush track is to be formed, and afriction wheel 44 connected to mandrel assembly is engaged with a friction Wheel 45 driven by motor 41. In the illustrated embodiment of my invention, the motor 41 drives the friction wheel 45 at a speed of five revolutions per' minute. In the specific e'xemplification of my invention, it was found that in two revolutions the desired relief polishing was accomplished. It will be noted that friction Wheel 46 at the loading and unloading station is not drivingly engaged with friction'wheel 45 of motor 41 and becomes engaged with it only when it is at the polishing station. After the brush track is produced by relief polishing at the polishing station, the turntable 37 is rotated by the operator to move the completed core and winding assembly 47 to the loading and unloading'station where it' is lifted off the mandrel assembly 39 and another core and winding assembly is placed in positon on the mandrel assembly'39. p I

In the illustrated embodiment of the invention, polishing disc 43 is driven by an air motor 49 pivotally supported on an arm 50 carried on bracket 51. In order to adjust the contact pressure that the polishing disc exerts against the winding, an adjustable counterbalanceweight 52 is attached to a balance arm 53'. When the balance weight 52 is positoned to provide the desired amount of pressure, it is secured by turning the knob 54. At the completion of the relief polishing operation, an air cylinder 55 is actuated to elevate the arm 50-and lift the polishing disc 43 out of engagement with the core andwinding assembly. When-the next winding and core assembly 48 is indexed into position at the work station, air cylinder 55 is then deenergized, rod 56 of the aircylinder. 55 dropping out of engagement with the arm so that the desired amount of contact pressure is now applied as determined by the position of the counterbalance weight 52 on the balance arm 53.

Thus, the method of producing my improved brush track arrangement for an adjustable sliding brush trans-, former involves relief polishing a portion of the winding of the core and winding assembly until the insulation coating on the wire is removed to expose the bare metallic conductor and to remove a substantially greater amount of the resin material than metallic conductor to form a concave-convex brush track. Although preferably I have employed a polishing disc of thermoplastic polyamide fibers impregnated with silicon-carbide grit, it will be understood that other polishing discs, such as fiber glass, that will remove substantially more resin material than metallic conductor may be employed.

An important advantage of the improved transformer and method for producing a brush track for an adjustable sliding brush transformer as described above is that the quality of the transformer and specifically the brush track is improved as compared with transformers of the prior art having brush tracks produced by lapping and grinding operations. It is possible with the improved arrangement to achieve significant manufacturing cost savings in transformers utilizing relatively fine wire as a result of the reduction in the number of rejects during manufacture.

From the foregoing description of the improved apparatus and method exemplifying my invention, it will be apparent that I have provided an improved variable transformer of the adjustable brush type. Although in the exemplification of my invention, the method was illustrated in conjunction with a brush track having convex contact surfaces, it will be appreciated that my method of producing brush tracks by relief polishing can also be employed in connection with brush tracks having flat surfaces to achieve undercutting between the flat contact surfaces. For example, in adjustable sliding brush transformers of the higher current ratings using conductor wire of relatively larger diameter size, the contact surfaces may be formed by removing the insulation by grinding the wire flat and then may be relief polished in accordance with the present invention. It will be obvious therefore to those skilled in the art that changes and modifications may be made without departing from the invention. It is therefore intended in the appended claims to cover all such changes and modifications that fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. An adjustable sliding brush transformer comprising: an annular core of magnetic material; a shell of insulating material disposed on said annular core; a winding of successively disposed adjacent" Wire turns wound on said shell and overlying said annular core; a relief-polished brush track including a series of convex contact surfaces on said successively disposed adjacent wireturns; a resin material bonding said portions of the turns forming said convex contact surfaces to said shell, said resin material presenting a series of concave surfaces along the brush track underspanning said series of convex contact surfaces; and at least one electrical brush for sliding electrical engagement with said convex contact surfaces of said winding whereby electrical contact between said brush and said winding is achieved by sliding movement of the brush along said convex contact surfaces.

2. An adjustable sliding brush transformer comprising: a core of magnetic material; a winding of successively disposed adjacent wire turns wound on said core; a reliefpolished brush track including a series of convex contact surfaces on said successively disposed adjacent Wire turns; resin insulating material disposed between said wire turns having said convex contact surfaces, said resin insulating material formed with seriesof concave surfaces along the brush track; and at least one electrical brush for sliding electrical contact with said convex contact surfaces whereby electrical contact between said brush and said winding is achieved by sliding movement of the brush along said convex contact surfaces.

References Cited UNITED STATES PATENTS 2,118,267 5/1938 Richter 338-174 XR 2,204,623 6/1940 Ruben 338159 2,619,537 11/1952 Kihn 336149 XR 2,759,081 8/ 1956 Mounteer 336149 XR 2,949,592 8/1960 Smiley 336148 LEWIS H. MYERS, Primary Examiner T. J. KOZMA, Assistant Examiner US. Cl. X.R. 

